What is Parish Clerk?

Legal Definition
In English law. An officer, in former times often in holy orders, and appointed to officiate at the altar; now his duty consists chiefly in making responses in church to the minister. By common, law he has a freehold in his office, but it seems now to be falling into desuetude. 2 Steph. Comm. 700; Mozley & Whitley.
-- Black's Law Dictionary